Optical materials using plastics are lightweight, hardly breakable, and excellent in dyeability as compared with optical materials made of inorganic materials such as glass. Therefore, plastic materials of various resins are widely used as optical materials for eyeglass lenses, camera lenses, and so on. Recently, due to an increased demand of users for higher performance and convenience, studies have continued on optical materials having such properties as high transparency, high refractive index, high Abbe number, low specific gravity, high heat resistance, and high impact resistance.
Examples of widely used optical materials include polythiourethane compounds obtained by polymerizing a polythiol compound and a polyisocyanate compound. However, when a polythiol compound and a polyisocyanate compound are reacted to prepare a polythiourethane-based optical material, the reactivity changes depending on the kinds of the polythiol compound and the polyisocyanate compound and the kind and content of the catalyst, which causes a problem that the polythiourethane-based optical material thus produced has appearance defects such as striae and/or bubbles.
As an alternative to the above, Korean Patent No. 1704951 discloses a method for preparing a polyurethane resin composition in which an alcohol compound is employed such that the ratio of hydroxyl groups to isocyanate groups is 10 to 20% by mole.